Mohamed Lahouaiej Bouhlel’s text messages were revealed as a 37-year-old man, who was said to be in the killer’s “entourage,” and an Albanian couple were arrested in France and questioned, officials said. A total of seven people have now been arrested in the investigation.

It was not immediately clear to whom the messages were sent.

French authorities believe Bouhlel, 31, who had a record of minor crimes, had only recently been radicalized, Prime Minister Manuel Valls told the Journal du Dimanche.

He was out to kill as many people as possible, said the manager of the company from which he rented his truck.

“The terrorist demanded the biggest vehicle we have — the heaviest, the most powerful, the most massive, to create the maximum number of victims,” the manager of the rental company Via Location told the Daily Mail.

Secretary of State John Kerry said Sunday that even the best counterintelligence operations would be hard pressed to prevent an attack like this one.

The difficulty of finding people like Bouhlel is “worse than the needle in the haystack,” Kerry told CNN.

French police initially detained Bouhlel’s estranged wife, but she was released Sunday.

Bouhlel’s brother said their family had no idea what he had in mind.

“That last day, he said he was in Nice with his European friends to celebrate the national holiday,” the brother, Jabeur, told Reuters in their native Tunisia.

He sent a photo in which “he seemed very happy and pleased, he was laughing a lot,” the brother said.

Jabeur, 20, told The Sunday Mirror newspaper: “When we heard about what was happening in Nice, we started to send him messages asking if he was all right. We here were sending him messages until 2 in the morning.”

Meanwhile, a US college student who had been missing since the attack was confirmed to be among the slain Sunday.

Nicolas Leslie, 20, of Del Mar, Calif., was a student at the University of California, Berkeley, and had been in Nice as part of a foreign-studies program.

Two other students participating in the program — Canada-based Ukrainian national Misha Bazelevsky, 22, and Estonian Rickard Kruusberg, 21 — were still missing Sunday night.